A 53-year-old Japanese woman underwent investigation of her heart murmur. A continuous abdominal bruit was heard. Blood gas analysis and chest X-ray showed congestive heart failure. Enhanced computed tomography of the pelvis showed a 10 x 4 cm hypervascular tumor in the retroperitoneal space. Cardiac catheterization disclosed a cardiac output of 13.2 L/min and a step-up of oxygen at the right common iliac vein. Abdominal aortic angiography showed an extremely vascular pelvic tumor and rapid filling of the inferior vena cava. This is a rare case of a highly vascular pelvic tumor causing high-output heart failure because of th massive arteriovenous shunting.